Glioblastoma (GBM)

Glioblastomas (GBMs) account for almost half of all cancerous brain tumors in adults. This brain cancer grows rapidly and can spread throughout the brain. New treatments, including tumor treatment fields and targeted therapies, help ease symptoms and slow cancer growth.


What is glioblastoma (GBM)?

Glioblastoma multiforme (GBM) is the most common type of malignant (cancerous) brain tumor in adults. Cancer cells in GBM tumors rapidly multiply. The cancer can spread into other areas of the brain as well. Rarely, the cancer spreads outside the brain to other parts of the body.

Glioma tumors like GBM start in glial cells. Glial cells are vital to nerve cell function. GBMs specifically form in glial cells called astrocytes. GBMs are the fastest-growing astrocytoma (tumor that forms in astrocytes).


Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy

How common is glioblastoma?

More than 13,000 Americans are diagnosed with GBM every year. GBM accounts for almost half of all cancerous brain tumors.

Who is at risk for glioblastoma?

GBM commonly affects people age 45 to 70. The average age at diagnosis is 64. Men have a slightly higher risk, but the disease affects all ages and genders.

These factors may increase your risk:

  • Exposure to chemicals, such as pesticides, petroleum, synthetic rubber and vinyl chloride.
  • Genetic, tumor-causing conditions, such as neurofibromatosis, Li-Fraumeni syndrome and Turcot syndrome.
  • Previous radiation therapy to the head.


Symptoms and Causes

What causes glioblastoma?

Experts don’t know why some people develop cancerous brain tumors, including GBM.

What are the symptoms of glioblastoma?

GBM symptoms tend to come on quickly. The growing tumor puts pressure on the brain, causing:


Diagnosis and Tests

How is glioblastoma diagnosed?

If your healthcare provider suspects a brain tumor, you may get these tests:

  • MRI or CT scan to look for brain tumors.
  • Biopsy to obtain a sample from a tumor and examine the tissue for cancer cells.

What are the types and grades of glioblastoma?

Healthcare providers use a grading system from 1 to 4 to indicate brain tumor growth. Grade 1 brain tumors grow slowly and are the least aggressive. Grade 4 tumors grow rapidly and are more aggressive.

GBMs are grade 4 by definition. GBM can be either primary or secondary. Primary GBM develops directly from glial cells. On the contrary, occasionally grade 1 glial tumors can progress to become GBMs; this is called secondary GBM.

Management and Treatment

What are the complications of glioblastoma?

GBM and its treatments can affect brain function. You may experience mood changes and memory problems. Most people with GBM eventually have to stop working and driving. You may need full-time care. These changes may make you feel anxious or depressed.

How is glioblastoma managed or treated?

Unfortunately, there isn’t a cure for GBM. Treatments focus on removing or shrinking the tumor to reduce symptoms.

The first step is surgery to remove the tumor (craniotomy), followed by radiation and chemotherapy. If surgery isn’t an option due to your health or the tumor location, radiation and chemotherapy can control the tumor.

GBM treatments include:

  • Radiation therapy: Radiation therapy uses S-rays to damage cancer cells so they can’t grow. You may need as many as 30 daily radiation treatments over six weeks.
  • Intensity modulated radiation therapy (IMRT): IMRT allows the delivery of radiation to the tumor while minimizing the radiation dose to the surrounding healthy brain tissue.
  • Stereotactic radiosurgery: Gamma knife radiosurgery is a type of advanced radiation therapy. (Despite the name, it is not a surgical procedure.) Highly focused X-ray beams precisely target the tumor, limiting damage to healthy tissue. Providers occasionally use this technique when GBM grows after receiving initial IMRT.
  • Chemotherapy: Chemotherapy medication circulates in your blood to kill cancer cells. You may receive chemotherapy at the same time as radiation therapy as well as after radiation therapy is completed.
  • Targeted therapy: Instead of chemotherapy, you may receive targeted therapy. This treatment targets certain cell changes that fuel cancer growth.
  • Tumor treatment fields (TTF): A wearable device sends low-intensity electric fields (TTFs) to the tumor through electrodes on the scalp. TTFs disrupt cancer cells, preventing them from multiplying and growing. Providers may consider this treatment after chemoradiation is complete.

Outlook / Prognosis

What is the prognosis (outlook) for people who have glioblastoma?

GBM is aggressive cancer that is difficult to treat. There isn’t a cure. Treatments ease symptoms and help you stay comfortable and prolong your life. There are many clinical trials underway to find new GBM treatments.

Therapies that target specific cancer cell genes show promise. Researchers are also looking at ways to deliver chemotherapy directly to the brain tumor. Your healthcare provider can determine whether a clinical trial is right for you.

Unfortunately, most people live on average 12 to 18 months after diagnosis. Only about 7% of people are still alive in five years.

Living With

When should I call the doctor?

You should call your healthcare provider if you experience:

  • Memory problems.
  • Seizures.
  • Severe headaches or vision problems.
  • Unexplained weight loss or nausea and vomiting.

What questions should I ask my doctor?

You may want to ask your healthcare provider:

  • Why did I get glioblastoma?
  • What is the best treatment for me?
  • What are the treatment risks and side effects?
  • What type of follow-up care do I need after treatment?
  • What are the chances that the cancer will come back or spread after treatment?
  • Should I look out for signs of complications?

A note from Cleveland Clinic

Finding out you have GBM can be difficult. The disease grows quickly and treatment is challenging. Researchers continue to look for new ways to treat GBM. For now, treatments can minimize symptoms and improve your quality of life. Talk to your healthcare provider about treatment options, including clinical trials.

Medically Reviewed

Last reviewed on 09/03/2021.

Learn more about our editorial process.

Appointments 866.588.2264